Breeding improved tomato varieties involves providing genetics that give an advantage to the grower, processor, consumer, or other members of the supply chain. The improvement may be in the form of field performance, disease resistance, factory performance, or a fruit quality characteristic. For a tomato variety to be suitable to be grown for processing, the variety must have a concentrated fruit setting and maturity, firm fruit, and sufficient rot tolerance to allow early fruit to remain rot-free while later fruit continues to develop and ripen.
Most commercial processing tomato varieties are hybrids resulting from a cross pollination of two true-breeding, inbred parents. Through the use of true-breeding lines, a hybrid is produced that often displays characteristics of each parent, and often demonstrates characteristics that are superior to either parent alone, or that allow a hybrid to mask inadequacies of the individual parents.
Processing tomato varieties combining resistance to verticillium wilt race 1 (Verticillium dahlia), fusarium wilt race 1 and 2 (Fusarium oxysporum pv lycopersici), root knot nematode (Meloidogyne incognita) and tomato spotted wilt virus (TSWV) are highly desirable in most climates around the world. Moreover, in humid regions such as Eastern North America, there is considerable disease pressure from bacterial diseases such as bacterial canker (Clavibacter michiganenesis michaganensis) and bacterial spot caused by various Xanthomonas species. Thus, varieties with resistance are in high demand by both growers and processors to ensure a productive crop cycle. Additionally, in recent years the industry has seen an increase in the presence of Late blight (Phytopthora infestans) which can have a devastating impact on the tomato crop.
An additional important contribution that tomatoes provide to the human diet is the antioxidant lycopene. Specifically, processed tomato products are the primary source of tomato intake in the US diet. Higher levels of lycopene are beneficial both from a nutritional standpoint and from a consumer perception and quality standpoint. Tomato varieties having higher levels of lycopene result in products with a deeper red color that can be considered an indicator of higher product quality. Thus, a tomato variety with a higher level of lycopene, and improved color in general can be valuable from both a nutritional standpoint and a quality standpoint. However, to be commercially viable, the tomato variety must perform acceptably in the field and factory as required by any other processing tomato variety.
Processing tomato quality parameters differ from those of fruit used in the fresh market. The processing characteristics are typically determined using a sample of hot-break tomato pulp or juice produced in a consistent manner to those familiar with the art. For example, a fixed mass of tomatoes may be cooked in a microwave oven for several minutes to halt any enzymatic breakdown of the sample, lost water is replaced, and the sample is pulped to remove skins and seed to produce a uniform juice sample. The juice sample can be analyzed for various quality parameters important to processing tomato including but not limited to gross viscosity measures such as juice Bostwick, soluble solids measures using a refractometer (° Brix), measures of acidity and pH, and measures of color (e.g. a Hunter a/b score). The value of these traits depends on the product that is being commercially produced by the processing factory. In some instances, a factory will put a higher value on a thick viscosity variety, whereas in other instances, a thin viscosity will make a superior product and is preferred.